15th International Workshop on Research and Education in Mechatronics (REM), Elgouna, Egypt, September 9-11, 2014 Using Elevator System Modelling and Simulation for Integrated Learning in Mechatronics Engineering Lutfi Al-Sharif1, Tarek A. Tutunji 2, Dana Ragab2, and Range Kayfi2 1 Mechatronics Engineering Department, The University of Jordan, Amman 11942, Jordan Mechatronics Engineering Department, Philadelphia University, Amman 19392, Jordan Corresponding e-mail: [email protected] 2 Abstract - Elevator systems offer ideal platforms for Mechatronics engineering education. Particularly, they offer an excellent opportunity for integrating the various mechatronics engineering disciplines, such as: electrical motors and actuators, power electronics and drives, control systems, system dynamics and kinematicsAlthough elevator systems have been used as learning platforms in engineeringeducation, the use of elevator modelling and simulation for a well-structured designprocess that includes analysis and synthesis is of interest. Furthermore, documenting such work can help mechatronics educators in using these models for their case studies in different courses. This paper reviews a Simulink/SimPowerSystems based platform that was built at Philadelphia University in order to allow students to practice and understand the principles of power electronics, drives systems, electrical machines and control system design by modelling real life elevator systems and running them. The learning outcomes achieved by the projects include enabling the students to model real life electromechanical systems, tune a PID controller that controls the speed of the elevator system, and design suitable power electronic drives to control the used motor. Keywords: mechatronics; education integration; power electronics; electrical machines; simulation; Matlab; Simulink; SimPowerSystems. I. INTRODUCTION The main criticism of conventional engineering education is twofold: the pure theoretical nature of the study material and the compartmentalisation of the different courses. Adding a practical hands-on dimension to the study material and integrating the different modules is considered a great enhancement to any engineering degree programme. Final year graduation projects and capstone courses offer the student the opportunity to gain practical experience in designing and building of 978-1-4799-3029-6/14/$31.00 ©2014 IEEE systems and of integrating the different courses studied during the undergraduate degree ([1], [2]). Elevators are vertical transportation systems that use motors and power electronics for mechanical movements.Various pieces of research have been published on the mechanical modelling of elevators, a good example of which can be found in [12]. Elevator systems havebeen used as learning platforms in many engineering courses but usually only in programming the controllers [7]. A good example on using a space elevator model to teach power electronics can be found in [8]. However, work that emphasize components’ selection, modules interactions, and system design using the modelling and simulation are very rare. The elevator simulation model described in this paper was built at the Philadelphia University during the academic year 2013/2014. One of its purposes was to integrate the three modules of: Power Electronics and Drive Systems, Electrical Machines and Automatic Control systems. The intention is to enhance and expand the scope of the model and use it in the future as a systematic tool within the teaching of these modules. This paper provides an overview of the model and provides some insight into the rationale for developing such a system. The use of Simulink as an engineering modelling tool has been discussed in a number of references ([3], [4], [5]). This paper emphasises the use of Simulink as an educational tool for a specific case study Section 2 lists the modules linked to theelevator model. It also highlights the learning benefits to the students. Section 3 specifies the main objectives and learning outcomes. Section 4 describes various sub-blocks of the model and the function of each block. Some results extracted from the model 15th International Workshop on Research and Education in Mechatronics (REM), Elgouna, Egypt, September 9-11, 2014 are shown in section 5. Conclusions are drawn in section 6. II. APPLICABLE KNOWLEDGE DISCIPLINES The developed elevator model offers the students hands on experience in a number of different disciplines. It also allows them to cross reference the different disciplines and understand the interrelationships among them. The model presented in this paper is linked (but not limited) to the following modules that are standard components of most under-graduate mechatronic engineering degrees: Electrical machines and actuators. Power electronics and drive systems. Modeling and simulation. Control system design. Kinematics. Due to the practical nature of Simulink, it offers a hands-on platform that allows the student to build engineering systems, run them and then observe the performance of the system. They can then troubleshoot problems in the system, improve the performance and fine tune the settings of the system.All of which are considered essential elements in a successful design process. It also provides them with the practical understanding of inter-relationships among the different disciplines. For example, studentswill use a power electronics drive to actuate an electrical motor, and can then find the system dynamics of the overall system and tune the close loop controller to meet certain system performance requirements (in the transient phase and in the steady state phase). The students are also forced to deal with and solve practical problems that are not usually addressed in the classical way of instruction, when courses are taught separately. For example, students have to introduce a saturation block into the controller in order to represent the fact that the power source feeding the dc motor has a finite voltage level and that the motor has a maximum torque specification. Another example, students must use a double bridge driving the dc motor in order to achieve driving and braking as needed. III. skills required for mechatronic system design. The following are the three main objectives of the described project: 1. 2. 3. The motor, power drive, and power mechanism selection are an integral part of mechatronics system design [2]. IV. DESCRIPTION OF THE MODEL This section describes the simulation model used in detail. A block diagram of the whole model is shown inFigure 1. Figure 2 shows the SIMULINK model of the system. It follows a modular approach to building the model. This allows the student to adopt a modular based approach to model building and practice the engineering principle of piecewise building and stepwise refinement [6]. The students can work in different teams, where each team member can independently work (in parallel) on one module, while still liaising with other members of the team on the overall design of the model. This approach teaches the students to follow the synergistic design approach often implemented when dealing with mechatronic systems. The model comprises the following four main modules: Controller, electrical drive, DC motor and mechanical system. 1. The Controller block. This is the Proportional-Integral (PI) block that contains the PI parameters and the signal pre-processing. This is directly linked to a course inautomatic control. Students learn the effect of varying the PI parameters and observe their result to the elevator speed behaviour. Students can then analyse the transient and steady-state responses on the elevator system. In order to get better insight, theinternal structure of this block is also provided to the students as shown inFigure 3.The use of the saturation block is used to demonstrate the practical issues of voltage/power limitations to the students. 2. The Electrical Drive block that contains the double six-pulse-controlled-rectifier bridges PROJECT OBJECTIVES AND LEARNING OUTCOMES The main goal of the elevator modelling and simulation project is to teach the students essential To equip the students with skills to model real life electromechanical systems. To enable the students to design closed control systems, such as PID, for electromechanical systems. To enable the students to select suitable actuators and power converters for elevator systems. 15th International Workshop on Research and Education in Mechatronics (REM), Elgouna, Egypt, September 9-11, 2014 used for driving and braking the DC motor and the firing pulses generators. This is very closely linked to a course on power electronics and drive systems. The internal structure of this block is shownFigure 4. Due to the complexity of this block it is further subdivided into three blocks: firing pulses generator, signal processing and the rectifier bridges. Figure 5 shows the rectifier block. The other two blocks are not shown here because of space limitation. 3. The DC-Motor block which contains the model of the dc motor used as the hoisting motor and the processing necessary to extract the torque from the motor and feedthe actual speed. This is closely linked to a course on electrical machines and actuators. Theinternal structure of this block is shown in Figure 6.During their work, students calculate the required speedtorque characteristics and can then select the appropriate motor from manufacturer’s data sheets. When the selection process is complete, students can enter the selected motor parameters in the SIMULINK block and verify the results. This motor selection and verification skill is essential to the mechatronic design process. 4. The Mechanical System block which contains the details of the system inertia (second moment of mass) referred to the low speed shaft (LSS), the passenger mass, the frictional model and the implementation of the rotational equivalent of Newton’s second law applied on the LSS. This is an ideal application of a course on system dynamics. Theinternal structure of this block is shown inFigure 7.The students can experiment with the mechanical system responses because they have direct access to the linear and rotational velocities and the linear displacement. They can change the system parameters (such as inertia, friction, and radius), observe the curves, and analyse the results. In SIMULINK, the Kinematics Generator block is used to generate the velocity profile for a one-floor journey of 4.5 m in this case, based on specified values of rated velocity, rated acceleration and rated jerk. This is closely linked to a course on dynamics. The relationship between the velocity and acceleration is highlighted using output scope plots from SIMULINK. This relationship is further linked to the mathematical foundations. Figure 1: Simplified block diagram. 15th International Workshop on Research and Education in Mechatronics (REM), Elgouna, Egypt, September 9-11, 2014 Figure 2: Simulink model of the elevator system. Figure 3: Controller. 15th International Workshop on Research and Education in Mechatronics (REM), Elgouna, Egypt, September 9-11, 2014 Figure 4: Electrical drive system. Figure 5: Controlled 6 pulse three phase bridge rectifier. 15th International Workshop on Research and Education in Mechatronics (REM), Elgouna, Egypt, September 9-11, 2014 Figure 6: Separately excited DC motor used as a hoist motor. Figure 7: Mechanical load. V. RESULTS The reference speed is entered into the system as a linear speed of the elevator car. The top rated speed of the elevator is 1.6 m/s. The rated acceleration is 1 m/s2 and the rated jerk is 1 m/s3. The kinematics generator is used to generate a reference speed profile for a one floor journey of 4.5 m. The reference speed profile is shown inFigure 8. Superimposed on it is the actual linear elevator car speed. The result is very good, but does not convey the true performance of the system in terms of stopping position accuracy. There is an error of around 50 mm in the overall displacement, which translates in the elevator into stopping inaccuracy. One of the common mistakes that the student makes when building the model is not to include a braking rectifier bridge. This leads to problems during the deceleration phase of the elevator journey, as shown in Figure 9. It is clear thatthe system is out of control during this phase, and it is slowing down under the influence of friction only. Furthermore, students can trace the signals throughout the system in order to better understand the controller actions, system dynamics, and interaction between the sub-systems. The analysis of the interaction between the blocks enforces the concept of integration in mechatronic systems Actual Speed ReferenceSpeed Figure 8: Actual and reference linear speeds for a one floor journey. 15th International Workshop on Research and Education in Mechatronics (REM), Elgouna, Egypt, September 9-11, 2014 Figure 9: Actual speed when no braking is present. These plots are shown inFigures 10, 11, and 12. The error, controller, drive, and motor signals are used to help students understand the inputs and outputs of each block. These are the outputs of themain blocks shown in Figure 1 and Figure 2. Figure 12: Drive output. Figure 12 shows the signal representing the output of the drive system. This is the signal that drives the motor and has units of volts and provides braking as well as driving. The fluctuations are due to the rectifiers effect. Figure 13 shows the torque output of the motor, which has fluctuation in it, and this is due to the nature of the voltage signal applied to the motor. Figure 10: Error signal. Figure 10 shows the error signal, which is the difference in speed between the reference velocity and the actual velocity. There is initially too much fluctuation in its value, but it eventually settles down to a smaller value. Figure 11 shows the controller output. Note that is resembles the error signal multiplied by the proportional gain in the PI controller. The integral part is used to minimize the steady state error Figure 13: Motor torque output. In addition, an integrator was added to the system output in order to observe the displacement. The results are shown in Figure 14. Students can then compare the velocity (Figure 8) and the displacement (Figure 14) and analyze the results. The target displacement is 4.5m which is the vertical distance between two levels. Actual Displacement Reference Displacement Figure 11: Controller output. Figure 14: Displacement output. 15th International Workshop on Research and Education in Mechatronics (REM), Elgouna, Egypt, September 9-11, 2014 VI. CONCLUSIONS There is a need within engineering education to offer the students a more hands-on approach in studying and integrating the various engineering modules. This enhances the student’s understanding of the various inter-relationships between the different disciplines and enables him/her to tackle practical types of problems not encountered within theoretical study. The integrative approach to studying the various modules counteracts the silo approach to teaching the different modules.. An elevator modelling and simulation platform has been built within Simulink/Matlab. It consists of four main modules commonly used in Mechatronics engineering: power electronics and drives, electrical machines and actuators, automatic control systems, kinematics and system dynamics. The platform allows students to gain a deep understanding of dynamic modelling of engineering systems and dealing with practical problems in control systems, such as the presence of saturation in most actuators and output devices. By adopting a modular approach in building the platform, the students practice the principle of piecewise building and stepwise refinement. It also allows them to work as teams, with different team members working on different modules within the platform. Therefore, the students experience the parallel design process and the interface requirements. The platform can be further expanded to be used for studying harmonics in electrical drive systems, power factor calculation in non-linear loads, the use of more advanced controllers (such as fuzzy logic controllers) and the measurement and modelling of electrical power consumption ([9], [10], [11]). ACKNOWLEDGEMENT This research was carried out during the sabbatical leave granted to Dr. Lutfi Al-Sharif by The University of Jordan for the period from September 2013 to August 2014. [1] [2] REFERENCES L. Al-Sharif,A. Saleem, T. A. Tutunji, “Mechatronic System Design: The Ideal Capstone Course”, Proceedings of the 7th International Symposium on Mechatronics and its Applications (ISMA ’10), 20th to 22nd April 2010, Sharjah, UAE. A. Saleem, T. Tutunji, L. 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